1. Field of the Invention
The present inventions are directed toward the field of manufacturing integrated circuits. The inventions are more particularly directed toward improved methods and apparatus for vaporization of deposition material in a deposition process system.
2. Description of the Related Art
Presently, aluminum is widely employed in integrated circuits as an interconnect, such as plugs and vias. However, higher device densities, faster operating frequencies, and larger die sizes have created a need for a metal with lower resistivity than aluminum to be used in interconnect structures. The lower resistivity of copper makes it an attractive candidate for replacing aluminum. There are well established techniques for depositing copper, including electroplating, chemical vapor deposition (xe2x80x9cCVDxe2x80x9d) and physical vapor deposition (xe2x80x9cPVDxe2x80x9d). A CVD process is desirable because it can often provide for a more conformally deposited layer. For example, chemical vapor deposition of copper may be achieved by using a liquid copper compound precursor known as Cupraselect(copyright), which has the formula Cu(hfac)L. Cupraselect(copyright) is a registered trademark of Schumacher of Carlsbad, Calif. The Cupraselect(copyright) consists of copper (Cu) bonded to a deposition controlling compound such as (hfac) and a thermal stabilizing compound (L). The (hfac) represents hexafluoroacetylacetonato, and (L) represents a ligand base compound, such as trimethylvinylsilane (xe2x80x9cTMVSxe2x80x9d).
During the CVD of copper using Cu(hfac)L, the precursor is vaporized and flowed into a deposition chamber containing a wafer. In the chamber, the precursor is infused with thermal energy at the wafer""s surface. At the desired temperature the following reaction is believed to result:
2 Cu(hfac)LCu+Cu(hfac)2+2Lxe2x80x83xe2x80x83(Eqn. 1)
The resulting copper (Cu) deposits on the upper surface of the wafer. The byproducts of the reaction (i.e., Cu(hfac)2 and (2L) can be purged from the chamber which is typically maintained at a vacuum during wafer processing.
One problem associated with using Cupraselect(copyright) for CVD can occur in the delivery of the material from its liquid storage ampoule to the process chamber in which the CVD occurs. Typically, the liquid Cupraselect(copyright) is first vaporized and mixed with a carrier gas such as Argon, Helium or another gas (usually an inert gas) between the ampoule and the process chamber. Vaporizers are incorporated into the delivery system and typically operate by altering one of two environmental conditions (temperature or pressure). Many vaporizers raise the temperature of the precursor to establish the desired state change. Unfortunately, raising the temperature too high can cause breakdown of the precursor and subsequent plating (deposition) in transfer lines between the ampoule and process chamber. One example of a known vaporizer is a CEM vaporizer manufactured by Bronkhurst of the Netherlands used to vaporize the precursor liquid. Unfortunately, these devices can clog after vaporizing only about 50-1500 g of Cupraselect(copyright). Such clogs can alter the deposition rate. For many wafer manufacturing applications, the vaporization rate is preferably repeatable from wafer to wafer.
After vaporization, Cupraselect(copyright) is often pumped into the process chamber along with an appropriate carrier gas. This pumping action can pull a high concentration of TMVS out of the Cupraselect leaving the less stable copper and (hfac) in the transfer lines between the ampoule, delivery system and process chamber. Under these conditions, undesirable plating or deposition is also likely to occur at various locations. For example, plating can occur near the vaporizer, valves, process chamber showerhead orifices and the like. Plating can change the dimensions of these system components which can degrade performance of the chamber and the resultant deposition layer. Additionally, unwanted plating may flake off during the deposition process which can render a processed wafer faulty or unusable. A maintenance cycle run on the process chamber to replace or clean the chamber can reduce wafer throughput.
As described in copending application Ser. No. 09/120,004, filed Jul. 21, 1998 and assigned to the assignee of the present application and incorporated herein by reference, to provide for repeatable deposition conditions, it is often desirable to create the precursor vapor as close to the process chamber as possible to reduce the likelihood of deposition at points in the delivery system, and to reduce the time and cost of purging the process chamber. In the apparatus of this copending application, a vaporizer is disposed directly on the lid of the process chamber which reduces the components used to deliver the precursor so as to reduce opportunities for clogging and to facilitate purging of the system when so needed.
In one aspect of the present inventions, improved methods and apparatus for vaporization of deposition material in a deposition process system are provided. For example, in the illustrated embodiment, a vaporizer includes a body defining a cavity having an outlet and a recessed inlet wherein the cavity outlet is larger than the recessed cavity inlet. The vaporizer body further defines a first passageway coupled to the inlet and adapted to carry a mixed flow of carrier gas and a liquid precursor to the cavity inlet. The passageway has a relatively short length and small width to form small particles of the liquid precursor and to inhibit recombination of the liquid precursor to larger droplets. The cavity is shaped to permit the mixed flow of carrier gas and liquid precursor to expand as it flows from the cavity inlet to the cavity outlet. As a consequence, the liquid precursor is dispersed by the carrier gas expanding through the cavity.
In the example of the illustrated embodiment, the vaporizer is disposed on the lid of a chemical vapor deposition chamber. In another aspect, the vaporizer further includes a hot plate disposed between a showerhead and the cavity outlet, and adapted to vaporize dispersed liquid precursor into vaporized material. The showerhead, disposed in the chamber lid in the illustrated embodiment, is adapted to distribute vaporized material for deposition onto a wafer or other workpiece.
In one aspect of the illustrated embodiment, clogging of the vaporizer may be reduced to increase throughput of the deposition system before purging or other cleaning may be indicated.
It should be understood that the preceding is merely a brief summary of one embodiment of the present inventions and that numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the inventions. The preceding summary, therefore is not meant to limit the scope of the inventions. Rather, the scope of the inventions are to be determined only by the appended claims and their equivalents.